1. Field of the Invention
The invention relates to the field of solar generators and in particular those embarked on spacecraft, such as satellites, for example.
2. Description of the Prior Art
Some solar generators have branches that are electrically connected in parallel at opposite first and second ends, respectively of positive and negative polarity, and each of which includes one or more photoelectric cells electrically connected in series and each covered on its front face with a protective window (or screen or filter).
The protective windows (or screens) are intended to protect the photoelectric cells from certain kinds of radiation, for example streams of protons and/or electrons, in order to guarantee a certain service life thereof. These protective windows (or screens) have to allow photons to pass through them, and are therefore generally made from a glass type material (for example a “coverglass” type material). As this material is not conductive, it tends to become charged, which sometimes causes localized electrical arcing known as a primary arc (or electrostatic discharge (ESD)) between a protective window and the photoelectric cell that it covers or an adjacent photoelectric cell.
This primary arc has been found to consist of two portions.
A first portion, known as the “blow-off” portion, takes the form of a current induced by the rapid discharging of the general capacitance of the system on which the solar generator is installed, for example a satellite.
A second portion, known as the “flash-over” portion, takes the form of a current induced by the slow discharging of the protective windows of at least some of the photoelectric cells, in accordance with a step by step propagation mechanism the propagation speed of which is of the order of 104 m/s. This propagation mechanism occurs not only from the protective is subject to the primary arc by reason of the plasma that is created between the protective windows of the cells, but also from the protective windows of the cells of adjacent branches to the protective window of the cell subject to the primary arc by reason of said plasma and of the circulation of the slow discharge current from the branch subject to the arc to the adjacent branches, via their electrical connections. The slow discharge current generally circulates via the second ends of the branches, of negative polarity, as their first ends are generally provided with current blocking means such as diodes.
This flash-over (or slow discharge) can lead to certain photoelectric cells being degraded if its duration exceeds a threshold that depends on the material from which these photoelectric cells are made. This is the case in particular if the photoelectric cells are made from a semiconductor material such as gallium arsenide (GaAs) and the duration of the flash-over (or slow discharge) is greater than approximately 100 μs. This degradation leads to a reduction in the service life of the photoelectric cells (and therefore a reduction in their reliability), which is a particular problem if they cannot be replaced.
Thus one object of the invention is to overcome the problem cited above.